x86, trace: Delete __trace_alloc_intr_gate()

Currently irq vector handlers for tracing are registered in both set_intr_gate()
 and __trace_alloc_intr_gate() in alloc_intr_gate().
But, we don't need to do that twice.
So, let's delete __trace_alloc_intr_gate().

Signed-off-by: Seiji Aguchi <seiji.aguchi@hds.com>
Link: http://lkml.kernel.org/r/52716E1B.7090205@hds.com
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>